Photonic network packet routing method and packet router for photonic network

ABSTRACT

A photonic network packet routing method includes the steps of optically encoding destination address information attached to an IP packet using light attributes, discriminating the encoded address information of the IP packet by optical correlation processing, switching to an output path for the IP packet based on a result of the discrimination, and outputting the IP packet labeled with prescribed address information on the output path selected by the switching step. A packet router for a photonic network includes a device for encoding by use of light attributes destination address information attached to an IP packet, a branching device for sending the IP packet having the encoded destination address information onto two paths, an address processing device for subjecting one IP packet received from the branching device to optical correlation processing and outputting a switch control signal based on a result of the discrimination, and a switch device for selectively outputting the packet by switching an output path of the other packet received from the branching device based on the address control signal from the address control device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of, and claims the benefitof priority under 35 U.S.C.§120 from, U.S. application Ser. No.11/613,873, filed Dec. 20, 2006, herein incorporated by reference, whichis a Divisional of U.S. Pat. No. 7,177,544, issued Feb. 13, 2007, hereinincorporated by reference, and claims the benefit of priority under 35U.S.C.§119 from Japanese Patent Application No. 11-355967, filed Dec.15, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photonic network packet routing method and apacket router for a photonic network that are adapted for use in aphotonic network utilizing optical fibers as transmission lines fortransmitting information among many locations and that, at the time oftransmitting packets labeled with destination addresses, distribute thepackets onto appropriate optical paths at nodes for combining multipleoptical pulses.

2. Description of the Prior Art

Photonic network technologies for point-to-point transmission ofinformation converted into optical signals have been applied to networksto create photonic networks. When, for example, the objective is toconfigure a network for transmitting Internet protocol (IP) packets overa photonic network, i.e., an IP-over-photonic network, photonic IProuters are required for switching the IP packets according to the IPaddresses.

FIG. 13 is a conceptual diagram of conventional photonic IP routing. Thediagram shows how a photonic IP router processes an IP packet groupconsisting of first, second and third packets (Packets #1, #2 and #3)respectively labeled with IP addresses Addresses #2, #3 and #1. WhenPacket #1, Packet #2 and Packet #3 are input in time series through anoptical signal input (IN) of the photonic IP router in the ordermentioned, the photonic IP router switches Packet #1 labeled with IPAddress #2 through a second output port (OUT 2), Packet #2 labeled withIP Address #3 through a third output port (OUT 3), and Packet #3 labeledwith IP Address #1 through a first output port (OUT 1). In other words,the function of the photonic IP router is to read the addresses of theIP packets and switch each packet to the port appropriate for itsaddress.

FIG. 14 schematically illustrates the configuration of a photonic IProuter 140 having N number of output ports. IP packets input through anoptical input port (IN) are sent along two branches to both an addressprocessing section 141 and a switching section 142.

In the address processing section 141, a photodetector 141 a convertseach IP packet into an electric signal, a signal processor 141 b readsits IP address and supplies the packet's routing information to acontroller 141 c. The controller 141 c uses the routing information toproduce a control signal specifying the destination (one of the 1s' toNth ports) of the packet and sends the control signal to the switchingsection 142.

In the switching section 142, an optical delay unit 142 a delays eachreceived packet and then forwards it to a 1×N optical switch 142 b forswitching each input to one of the N number of output ports. When eachIP packet is input to the 1×N optical switch 142 b, the 1×N opticalswitch 142 b is switched to the appropriate port by the control signalfrom the controller 141 c of the address processing section 141. The IPpacket is therefore output from the output port appropriate for the IPaddress of the IP packet.

Thanks to recent advances in photonic device technology, the opticalswitch 142 b can have a switching speed faster than 1 ns (equivalent to1 GHz). Switching speeds faster than 100 Ps have been achieved in thelaboratory.

Still, increasing the switching speed of the optical switch 142 b doesnot increase the routing speed of the photonic IP router 140 as a wholebecause the processes between reading the IP address of thephotoelectrically converted optical signal and control of the opticalswitch 142 b by the controller 141 c are conducted electrically. Sincethe arrival of the control signal from the controller 141 c at theoptical switch 142 b is therefore delayed, each IP packet sent to theswitching section 142 must therefore be delayed by the same amount bythe optical delay unit 142 a so that it will arrive at the 1×N opticalswitch 142 b at the same time as the corresponding control signal. Therouting speed is slowed in proportion to the delay.

The main object of this invention is to provide an ultra-fast packetrouting method and a packet router capable of reading IP addresses fromoptical signals.

The present invention, accomplished for overcoming the foregoingproblem, achieves high-speed routing by enabling all processing of IPpacket addresses in the processing section (processing for selecting thecourse along which IP packets are to proceed) to be conducted opticallyrather than electrically, thereby eliminating a major roadblock torouting speed enhancement.

SUMMARY OF THE INVENTION

This invention achieves this object by providing a photonic networkpacket routing method comprising a step of optically encodingdestination address information attached to an IP packet using lightattributes, a step of discriminating the encoded address information ofthe IP packet by optical correlation processing, a step of switching toan output path for the IP packet based on a result of thediscrimination, and a step of outputting the IP packet labeled withprescribed address information on the output path selected by theswitching step.

The optically encoding of the destination address information attachedto the IP packet can be conducted by dividing an optical pulse output bya pulse source into multiple chip pulses having a prescribed delay timetherebetween, imparting the individual chip pulses with phase shifts of“0” or “π” relative to a light carrier phase of the chip pulses, andrecombining the divided optical chip pulses.

The optically encoding of the destination address information attachedto the IP packet can be conducted by dividing an optical pulse intomultiple chips having a prescribed delay time therebetween, changingnormalized intensity of the individual chip pulses to “1” or “0”, andrecombining the divided optical chip pulses.

The discrimination of the encoded address information by opticalcorrelation processing is conducted by subjecting the combined chippulses to matched filtering, effecting threshold processing on a centerpeak value of a generated autocorrelation function, and opticallyregenerating the obtained “0” or “1”.

The photonic network packet routing method can also comprise a step ofdividing an IP packet having encoded address information in two, a stepof sending one of the divided IP packets onto a number of arms equal toa number of address entries, a step of simultaneously conducting opticalcorrelation processing on all arms in parallel to discriminate addressinformation from an optical code in the packet containing the addressinformation, selecting an IP packet output path based on a result of thediscrimination, and outputting the other IP packet on the selectedoutput path.

The optical code of one of the two divided IP packets is discriminatedby optical correlation processing and the discriminated signal is usedeither in its unmodified form as an optical signal or after conversionto an electric signal, to open a gate of a prescribed output path.

This invention also provides a packet router for a photonic networkcomprising means for encoding by use of light attributes destinationaddress information attached to an IP packet, branching means forsending the IP packet having the encoded destination address informationonto two paths, address processing means for subjecting the one IPpacket received thereby from the branching means to optical correlationprocessing to discriminate its address information and outputting aswitch control signal based on a result of the discrimination, andswitch means for selectively outputting the other packet by switching anoutput path of the other packet received from the branching means basedon the address control signal from the address control means.

The means for attaching an optical code to the address information ofthe IP packet can be means comprising multiple tunable taps for dividinga light pulse output by a pulse source into a prescribed number ofoptical chip pulses, optical phase shifters for imparting phase shiftsof “0” or “π” to each divided chip pulse, and a combiner for recombiningthe divided optical chip pulses.

The means for attaching an optical code to the address information ofthe packet can be means comprising multiple tunable taps for dividing alight pulse output by a pulse source into a prescribed number of opticalchip pulses, gate switches for changing optical intensity of the chippulses to “1” or “0”, optical phases shifters for imparting phase shiftsto the divided optical chip pulses, and a combiner for recombining thedivided optical chip pulses.

The address processing means can be means comprising means for sendingthe one IP packet sent onto one path by the branching means onto anumber of arms equal to the number of address entries, and decodersprovided on the individual arms for outputting a switch control signalwhen the decoder's own code and the code of an IP packet coincide.

The switch means comprises means for sending the other IP packet sentonto the other path by the branching means onto a number of arms equalto the number of output ports and an optical gate provided on each armthat opens in response to a switching control signal from the decoder tooutput the IP packet onto the arm.

The packet router for a photonic network can comprise a combiner forcombining an IP packet output through a prescribed path with a pulsesignal for control adjusted to generate an optical pulse at a portionwhere it is desired to convert the optical code and a nonlinear opticalmedium for converting the combined signal into a prescribed optical codeby cross-phase modulation.

Thus, in the present invention, destination address information attachedto IP packets is optically encoded and the optical signal is read “asis” without conversion. Processing can therefore be conducted morerapidly by the conventional method in which address information isconverted to electric signals for reading.

Faster processing is also achieved by sending the optical code of eachpacket including address information onto a number of arms equal to thenumber of address entries and simultaneously conducing opticalcorrelation processing on all arms in parallel.

The above and other features of the present invention will becomeapparent from the following description made with reference to thedrawings.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the node of a photonic networkincluding a photonic IP router that is an embodiment of the presentinvention.

FIG. 2 is a block diagram schematically illustrating the configurationof a transmitter for transmitting IP packets labeled with IP addresseswithin the network of FIG. 1.

FIG. 3( a) is a time waveform characteristic diagram of the pulse traingenerated by the transmitter.

FIG. 3( b) is a frequency spectrum characteristic diagram of the signalgenerated by the transmitter.

FIG. 4 is a block diagram schematically illustrating the configurationof an optical bipolar encoder for encoding by “0”, “π” phase shift.

FIG. 5 is a diagram showing the characteristic of an 8-chip opticalbipolar code generated by the optical bipolar encoder of FIG. 4.

FIG. 6 is a block diagram showing a photonic IP router that is a firstembodiment of the invention.

FIG. 7( a) is a diagram showing the characteristic of a decoded signalwaveform output by the optical encoder when the encoder's own code andthe code of an input signal coincide.

FIG. 7( b) is a diagram showing the characteristic of a decoded signalwaveform output by the optical encoder when the encoder's own code andthe code of an input signal do not coincide.

FIG. 8 is block diagram schematically illustrating an optical unipolarencoder for encoding by “0”, “1” pulse intensity.

FIG. 9 is a block diagram showing a photonic IP router that is a secondembodiment of the invention.

FIG. 10 is a block diagram showing a photonic IP router that is a thirdembodiment of the invention.

FIG. 11( a) is a block diagram showing an example of a converter forconversion of IP packet “0”, “π” optical codes.

FIG. 11( b) is a diagram illustrating the operating principle of opticalcode conversion conducted by the optical code converter of FIG. 11( a).

FIG. 12 is an explanatory diagram showing how an IP packet “0”, “1”optical code is converted by the invention.

FIG. 13 is a schematic diagram of conventional photonic IP routing(three output ports).

FIG. 14 is a functional block diagram schematically illustrating aconventional photonic IP router.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of packet routers for photonic network utilizing thephotonic network packet routing method of the present invention will nowbe explained with reference to the attached drawings.

FIG. 1 shows the basic architecture of a packet router for a photonicnetwork configured for use in an IP-over-photonic network fortransmitting Internet protocol (IP) packets. Designated by referencenumeral 1 is a photonic IP router that receives IP packets 3 . . . sentfrom a transmitter 2 over an optical fiber transmission line 4 andswitches each for output over one of three transmission lines: atransmission line 5 a (first output; OUT 1), a transmission line 5 b(second output; OUT 2) and a transmission line 5 c (third output; OUT3). The photonic IP router 1 thus has 1×3 routing capability.

The transmitter 2 maps the address information of the each IP packet 3in code (combination of 0, π), labels the IP packet 3 with the mappedaddress information, and outputs the IP packet 3 on the optical fibertransmission line 4. For instance, the IP packet 3 a is labeled with“0π0π0π0π” as second address information (Address #2), the IP packet 3 bis labeled with “0π0π0ππ0π0” as third address information (Address #3),and the IP packet 3 c is labeled with “0ππ000π0” as first addressinformation (Address #1).

The optical signal input to the photonic IP router 1 through the opticalfiber transmission line 4 is sent along two branches to both an addressprocessing section 6 and a switching section 7. In the addressprocessing section 6, an optical processor 6 a, which processes theoptical signal without modification, reads the IP address informationand outputs a signal for switching control. The signal for switchingcontrol produced by the optical processor 6 a is forwarded to aphotodetector 6 b that converts it to a high frequency electric signalthat it supplies to the switching section 7 as a switching controlsignal. Since the address processing section 6 of the photonic IP router1 conducts the reading of address information, reference to addressesfor selecting a path and the output of the switching control signaloptically, it enables a marked shortening of processing time.

The IP packets 3 . . . sent to the switching section 7 are received byan optical delay unit 7 a. The optical delay unit 7 a imparts them witha time delay proportional to the difference in the lengths of the lightpaths of the address processing section 6 and the switching section 7and then supplies them to an optical switch 7 b. Based on the switchingcontrol signals received from the address processing section 6, theoptical switch 7 b switches each IP packet 3 to the output portappropriate for its IP address. For example, the IP packet 3 c labeledwith the first address information is switched to the first output(transmission line 5 a), the IP packet 3 a labeled with the secondaddress information is switched to the second output (transmission line5 b), and the IP packet 3 b labeled with the third address informationis switched to the third output (transmission line 5 c).

The process for labeling the IP packets 3 . . . with address informationwill now be explained in detail with reference to the detailedarchitecture of the transmitter 2 shown in FIG. 2.

A mode-locked laser (MLLD) 2 b supplied with a signal from a 10 GHzgenerator 2 a serves as the coherent light source that produces a pulsetrain with a repetition frequency of 10 GHz, a half value width of 2 psand a center frequency of λ. The time waveform of the pulse train isshown in FIG. 3( a) and its frequency spectrum characteristic in FIG. 3(b). This pulse chain is divided into two pulses, one for producingaddresses and the other for producing data. One of the pulses isdecelerated in its repetition rate up to the packet rate by a timingsignal in an intensity modulator (EOM) 2 c and supplied to an opticalencoder 2 d, where addresses are imparted thereto as optical codes in acompletely optical manner.

The other pulse is modulated by an intensity modulator (EOM) 2 e inaccordance with packet data 3′, combined with an optical code producedby the optical encoder 2 d, amplified by an amplifier 2 f, and output onthe transmission line 4 as IP packets 3.

As an example, FIG. 4 schematically illustrates the architecture of anoptical encoder 2 d consisting of a PLC-type 8-chip optical bipolarencoder. The optical encoder 2 d can be used as both an encoder and adecoder.

An optical pulse entering the optical encoder 2 d is split by the actionof tunable optical taps 41 . . . and optical delay lines 42 . . .connected to the tunable optical taps 41 . . . into two or more chips(eight chips in this embodiment) of equal intensity having a delay timebetween taps of 5 ps. The optical carrier phases of the individual chippulses are imparted with phase shifts of “0” or “7” by an optical phaseshifters 43 . . . . The chip pulses are then combined by a combiner 44to produce an 8-chip optical bipolar code. The combination of phaseshifts imparted corresponds to one code. The desired optical bipolarcode can thus be produced by controlling each optical phase shifter 43in accordance with the address. FIG. 5 shows an example of a produced8-chip optical bipolar code. Pulses of 2 ps half value width separatedby intervals of 5 ps have carrier phases of 0, π, 0, π, 0, π, 0, π.

A first embodiment of the photonic IP router 1 that receives the IPpackets labeled with address information in the foregoing manner isshown in FIG. 6. The IP packets input on the transmission line are sentalong two branches to both the address processing section 6 and theswitching section 7.

The IP packets received by the address processing section 6 are furthersent along a number of arms equal to the number of addresses (three inthis embodiment). On the arms, the IP packets are simultaneously decodedby match-filtering in optical decoders 61 a, 61 b, 61 c, and convertedto electric signals by photodetectors 62 a, 62 b 62 c. As pointed outabove, the optical decoders 61 a, 61 b, 61 c can be configuredidentically to the PLC-type 8-chip optical bipolar encoder shown in FIG.4. Configuring the optical decoders 61 a, 61 b, 61 c as photonicprocessors enables the reading of address information and the productionof the signal for switching control to be processed in a wholly opticalmanner.

Thus, as explained in the foregoing, the present invention conductsaddress processing by sending the address information-bearing opticalcode of each packet along a number of arms equal to the number ofaddress entries and conducting optical correlation processing withrespect to the optical codes on all arms simultaneously and in parallel.The processing can therefore be conducted rapidly.

FIG. 7 shows an example of the decoded signal waveform output by theoptical decoders 61 a-61 c. When the decoder's own code and the code ofthe input signal coincide, the output waveform has a high peak (FIG. 7(a)). When the decoder's own code and the code of the input signal do notcoincide, no high peak value is present in the output waveform (FIG. 7(b)). Therefore, an optical signal having a high peak is output by one ofthe optical decoders 61 a-61 c only when the code denoting addressinformation of the input IP packet coincides with the optical decoder'sown code. Threshold processing is conducted to discriminate whether theoutput optical signal meets the requirements of a switching controlsignal. Furthermore, the output of the optical decoders is subjected totime gate processing to cut off the center part and eliminate side-lopesof the correlation waveform. This can ensure the threshold processingfor determining coincidence or noncoincidence of addresses. The timegate processing can be realized using a semiconductor gate switchdevice.

An IP packet received by the switching section 7 is sent to an opticaldelay unit 71 where it is imparted with a time delay proportional to thedifference in the lengths of the light paths of the address processingsection 6 and the switching section 7. The delayed IP packet is sentalong three arms connected with optical gates 72 a, 72 b, 72 c. Theoptical gates 72 a-72 c function as optical switches whose gates openonly upon receiving a switching control signal from the addressprocessing section 6 and stay closed at all other times. Each gate(ON-OFF switch) can, for example, be constituted as an LiNbO₃ intensitymodulator. Here, the optical delay unit 71 serves as an optical buffermemory that temporarily holds the packet in the optical region duringthe time of the address processing.

When the photonic IP router 1 configured in the foregoing mannerreceives the IP packet labeled with the first address information, onlythe optical decoder 61 a outputs an optical signal having a high peakvalue and, as a result, only the photodetector 62 a outputs a switchingcontrol signal. The optical gate 72 a therefore opens to send the IPpacket to the first output port. When the IP packet labeled with thesecond address information is received, only the optical decoder 61 boutputs an optical signal having a high peak value and, as a result,only the photodetector 62 b outputs a switching control 10 signal. Theoptical gate 72 b therefore opens to send the IP packet to the secondoutput port. Similarly, when the IP packet labeled with the thirdaddress information is received, only the optical decoder 61 c outputsan optical signal having a high peak value and, as a result, only thephotodetector 62 c outputs a switching control signal. The optical gate72 c therefore opens to send the IP packet to the third output port.

In the foregoing embodiment, encoding of the destination addressinformation attached to the packet is conducted using “0” and “π” phaseshifts. Next, an embodiment will be described with reference to FIG. 8in which the optical encoding is conducted using “0” and “1” based onpulse intensity.

A pulse entering an optical encoder 2 d′ is imparted with a prescribedtime delay by an optical delay unit 42′ connecting two tunable taps 41′and is divided into 8 chip pulses of equal intensity. The opticalintensities of the 8 chip pulses are changed to “0” or “1” by an opticalgate switch 45 and the chip pulses are then combined by a combiner 44′to produce an 8-chip optical intensity code. The imparted pulseintensity pattern corresponds to one code.

As in the embodiment using “0”, “π” encoding, when the IP packets havingdestination address information encoded with the aforesaid “0” and “1”are received by the address processing section, they are sent along twobranches to both the address processing section and the switchingsection (see FIG. 6). In the address processing section, the opticalcodes of the IP packets including address information are sent along anumber of arms equal to the number of address entries. On the arms, theoptical signals are decoded by match-filtering in decoders. A signalhaving a high peak is output by the decoder only when the input opticalcode and the code of the optical decoder coincide. The optical decoderhas the same configuration as the optical encoder.

An IP packet received by the switching section is sent to an opticaldelay unit where it is imparted with a time delay proportional to thedifference in the lengths of the light paths of the address processingsection and the switching section. The delayed IP packet is sent alongoutput port arms. Each arm has an optical gate connected with one of thedecoders. The gate of the arm opens to output the IP packet only wheninput with a switching control signal from the decoder of the addressprocessing section.

FIG. 9 is a block diagram showing a second embodiment of the photonic IProuter. The photonic IP router 1′ of FIG. 9 adopts the same means as therouter of the first embodiment for decoding encoded address informationof input IP packets and controlling the optical switches by switchingcontrol signals based on the decoded signals. As explained in thefollowing, the photonic IP router 1′ differs from that of the firstembodiment in ability to suppress input optical signal loss. Constituentelements similar to those of the router of the first embodiment areassigned like reference symbols and will not be explained again here.

An IP packet received by the photonic IP router 1′ is sent along twobranches. The IP packet sent to a switching section 7′ goes to anoptical delay unit 71 where it is imparted with a time delayproportional to the difference in the lengths of the light paths of anaddress processing section 6′ and the switching section 7′. The delayedIP packet is sent to a first optical switch 73 a. When the addressinformation of the IP packet is such that it should be sent to the firstoutput port, the first optical switch 73 a has received a switchingcontrol signal from a photodetector 62 a of the address processingsection 6′ and the IP packet is output from an A port of a first opticalswitch 73 a and sent to a first output port.

When the address information of the IP packet is not such that it shouldbe sent to the first output port, the first optical switch 73 a has notreceived a switching control signal from the photodetector 62 a of theaddress processing section 6′ and the IP packet is output from a B portof the first optical switch 73 a and sent to a second switch 73 b.

When the address information of the IP packet is such that it should besent to the second output port, the second optical switch 73 b hasreceived a switching control signal from a photodetector 62 b of theaddress processing section 6′ and the IP packet is output from an A portof a second optical switch 73 b and sent to a second output port. The1×2 optical switches (the first and first optical switches 73 a, 73 b)can be constituted as LiNbO₃ Mach-Zehnder type dual output intensitymodulators.

When the address information of the IP packet is not such that it shouldbe sent to either the first output port or the second output port, it isoutput from a B port of the second switch 73 b and sent to a thirdoutput port.

The photonic IP router 1′ of the second embodiment uses two-outputswitches (port changeover switches) as the switches of the switchingsection 7′ and, therefore, unlike the photonic IP router 1 according tothe first embodiment, does not constantly waste two-thirds of the energyconsumed by the switching section. The second embodiment thus provides alow-loss photonic IP router.

FIG. 10 is a block diagram showing a third embodiment of the photonic IProuter. The photonic IP router 1″ of FIG. 10 adopts the same means asthe routers of the first and second embodiments for decoding encodedaddress information of input IP packets and controlling the opticalswitches by switching control signals based on the decoded signals. Asexplained in the following, the photonic IP router 1″ differs from thatof the first and second embodiments in its feature of effecting opticalswitch control without converting the optical signals to electricsignals, thereby eliminating operational delay caused by using electricsignals converted from optical signals for optical switch control.Constituent elements similar to those of the routers of the first andembodiments are assigned like reference symbols and will not beexplained again here.

An IP packet received by the photonic IP router 1″ is sent along twobranches. The IP packet sent to a switching section 7″ passes through afirst optical circulator 74 a to a first nonlinear optical loop mirror(NOLM #1) 75 a. The first nonlinear optical loop mirror 75 a is composedof a first directional combiner 76, an optical fiber 77 formed into aloop, and a second directional combiner 78 located at an appropriatepoint on the optical fiber 77. Upon reaching the first directionalcombiner 76, the IP packet is divided into a component travelingclockwise in the optical fiber 77 and a component travelingcounterclockwise therein. After making one rotation, the components arecombined by the first directional combiner 76. The arrangement ispredefined such that the IP packet combined by the first directionalcombiner 76 normally (when no control signal is applied to the seconddirectional combiner 78) is output onto an arm on the right side(opposite from the input side) of the first nonlinear optical loopmirror 75 a.

When an optical decoder 61 a of an address processing section 6″ readthe address information and output a signal for switching control, thesignal for switching control, supplied to the switching section 7″ stillin optical form, passes through a first optical delay unit 71 a to thesecond directional combiner 78 of the first nonlinear optical loopmirror 75 a. Then when a switching control signal is input through thesecond directional combiner 78 at proper timing relative to the lightwave traveling clockwise in the optical fiber 77, the phase of theoptical signal traveling clockwise is changed by cross-phase modulation.Owing to this phase change, the IP packet combined by the firstdirectional combiner 76 is output on an arm on the left side (inputside) of the first nonlinear optical loop mirror 75 a.

Thus, the optical signal (IP packet) output from the first nonlinearoptical loop mirror 75 a is switched to the left or right depending onwhether or not a switching control signal from the address processingsection 6″ is present at the first nonlinear optical loop mirror 75 a.Therefore, when address information of an IP packet input to thephotonic IP router 1″ is such that the IP packet should be sent to afirst output port, the IP packet is returned from the first nonlinearoptical loop mirror 75 a to the first optical circulator 74 a and issent to the first output port (OUT 1) by the first optical circulator 74a.

When the address information of an IP packet is not such that the IPpacket should be sent to the first output port, the IP packet is sentonto the arm on the right side (opposite from the input side) of thefirst nonlinear optical loop mirror 75 a and then passes through asecond circulator 74 b to a second nonlinear optical mirror (NOLM #2) 75b. The second nonlinear optical mirror 75 b is also composed of a firstdirectional combiner 76, an optical fiber 77 formed into a loop, and asecond directional combiner 78 located at an appropriate point on theoptical fiber 77. Upon reaching the directional combiner 76, the IPpacket is divided into a component traveling clockwise in the opticalfiber 77 and a component traveling counterclockwise therein. Aftermaking one rotation, the components are combined by the firstdirectional combiner 76. The arrangement is predefined such that the IPpacket combined by the first directional combiner 76 normally (when nocontrol signal is applied to the second directional combiner 78) isoutput onto an arm on the right side (opposite from the input side) ofthe second nonlinear optical loop mirror 75 b.

When an optical decoder 61 b of the address processing section 6″ readthe address information and output a signal for switching control, thesignal for switching control, supplied to the switching section 7″ stillin optical form, passes through a second optical delay unit 71 b to asecond directional combiner 78 of the second nonlinear optical loopmirror 75 b. Then when a switching control signal is input through thesecond directional combiner 78 at proper timing relative to the lightwave traveling clockwise in the optical fiber 77, the phase of theoptical signal traveling clockwise is changed by cross-phase modulation.Owing to this phase change, the IP packet combined by the firstdirectional combiner 76 is output on an arm on the left side (inputside) of the second nonlinear optical loop mirror 75 b.

Thus, the optical signal (IP packet) output from the second nonlinearoptical loop mirror 75 b is switched to the left or right depending onwhether or not a switching control signal from the address processingsection 6″ is present at the second nonlinear optical loop mirror 75 b.Therefore, when address information of an IP packet input to thephotonic IP router 1″ is such that the IP packet should be sent to asecond output port, the IP packet is returned from the second nonlinearoptical loop mirror 75 b to the second optical circulator 74 b and issent to the second output port (OUT 2) by the second optical circulator74 b.

When the address information of an IP packet is not such that the IPpacket should be sent to either the first output port or the secondoutput port, the IP packet is sent through an arm on the right side(opposite from the input side) of the second nonlinear optical loopmirror 75 b to a third output port.

Since the photonic IP router 1″ according to the third embodiment usesnonlinear optical loops (NOLMs) as a light-to-light 1×2 switch, switchcontrol can be conducted directly by light, without converting thesignals for switching control into electrical signals. A photonic IProuter not dependent on electric circuitry likely to cause a bottleneckcan therefore be realized.

The photonic IP routers 1, 1′ and 1″ according to the first to thirdembodiments were all explained with regard to the case of generating IPaddresses using pulse code. The present invention is, however, notlimited to this method of generating the IP addresses attached to the IPpackets. Generally, IP addresses can be encoded by optical signals thatcan discriminate between coincidence and noncoincidence by correlationprocessing in the optical region.

As explained in the foregoing, the switch section is controlled byswitching control signals from the address processing section so as toswitch every IP packet input thereto to the output port appropriate forits IP address, whereafter the IP packet is transmitted to the nextnetwork node as a prescribed optical pulse. In some cases the opticalcode of the IP packet may have to be converted and the header rewritten.

FIG. 11( a) is a block diagram showing an example of a converter for usein the case where the optical code of the IP packet is a “0”, “π”phase-shift code.

IP packets requiring code conversion output by an IP router 81 are sentto a combiner 82. A λc pulse signal different from the IP packet is sentfrom a pulse source 83 to an optical encoder 84 as control light. In theoptical encoder 84, adjustment is effected with respect to the inputpulse signal for producing an optical pulse at the portion where theoptical code was converted. The so-adjusted pulse signal is combinedwith the IP packet in the combiner 82 and the combined signal isdirected into a nonlinear optical medium 85 to produce a cross-phasemodulation effect. A semiconductor optical amplifier, optical fiber orthe like can be used as the nonlinear optical medium.

The pulse consisting of the IP packet overlaid on the control light issubjected to phase modulation satisfying the relationship represented bythe following Equation (1). The desired phase modulation can thereforebe achieved by regulating the power and wavelength of the control light,the length of the nonlinear optical medium and the like.

$\begin{matrix}{{{\phi_{\max}(t)} = {\frac{4\;\pi\; n_{2}}{\lambda_{s}A_{eff}}{\int_{0}^{L}{{P\left( {t - {\tau\; z}} \right)}\ {\mathbb{d}z}}}}}{where}{\tau = {\frac{1}{V_{c}} - \frac{1}{V_{s}}}}} & (1)\end{matrix}$

(φ_(max)(t): phase modulation amount

λ_(s) (nm): signal light wavelength

n₂ (1/W/m²): nonlinearity coefficient

A_(eff) (m²): effective area

P(t): control light wavelength

τ(s/m): propagation difference of control light and signal light perunit length

L(m): length of nonlinear optical medium

V_(c) (m/s): signal light speed

V_(S) (m/s): control light speed

An IP packet with a converted optical code is obtained by passing thephase-modulated IP packet through an optical filter optical filter 86.

FIG. 11( b) is a diagram illustrating the operating principle of opticalcode conversion conducted by the optical code converter of FIG. 11( a).

The optical encoder 84 is adjusted to produce control pulses at aportion corresponding to two pulses of the latter half desired to beconverted. The optical signal of this control pulse is combined with theoptical signal to be modulated in the combiner 82 and is converted intoa [00 φmax φmax] optical code by interaction in the nonlinear opticalmedium 85. Utilizing the relationship represented by Equation (1), thecontrol light power, wavelength, length of the nonlinear optical mediumand the like are adjusted to make φ max equal to π. By this, the [0000]optical code can be converted to a [00ππ] optical code.

The foregoing also essentially applies when the optical code of the IPpacket is a “0”, “1” intensity code, i.e., the optical encoder 84 isadjusted to produce control light having a control pulse [0011] at aportion corresponding to two pulses of the latter half desired to beconverted.

When an IP packet having a code [1111] is directed into a loop mirror82′ (FIG. 12) serving as a combiner, it is divided into clockwise andcounterclockwise components. The control light sent from the opticalencoder 84 proceeds to the left in the loop mirror 82′ and combines withthe optical code of the IP packet. The optical code traveling in thesame direction as the control light has its phase changed to φ max byinteraction in the nonlinear optical medium. Utilizing the relationshiprepresented by Equation (1), the control light power, wavelength, lengthof the nonlinear optical medium and the like are adjusted to make φ maxequal to π. By this, the [1111] optical code can be converted to a[1100] optical code.

Since this invention thus enables all aspects of IP packet codeconversion to be conducted optically, it is capable of achieving opticalcode conversion of terabit-class high-speed pulse trains.

As explained in the foregoing, the photonic network packet routingmethod according to the present invention labels packets withdestination address information encoded using light attributes and, atevery node of the photonic network receiving the packets, sends theaddress information of each packet onto a number of arms equal to thenumber of output paths, conducts parallel discrimination by opticalcorrelation processing simultaneously on all arms, and switches thepacket to an output path based on the result of the discrimination.Packet routing can therefore be conducted at higher speed than by theconventional packet routing method in which switching to the outputpaths is done in accordance with address information after conversionfrom optical to electric address information. In particular, since thepacket routing method of the present invention enables application ofphotonic technology up to the point of transmission function, it can beexpected to be widely utilized as a fundamental technology for realizingan ultra-high speed, high-functionality photonic network.

In the packet router for a photonic network according to the presentinvention, each packet labeled with optically encoded destinationaddress information using light attributes is sent by branching meansover two separate paths to an address control means and a switch means,the address control means conducts optical correlation processing todiscriminate the address information of the one packet received therebyfrom the branching means and outputs an address control signal based onthe result of the discrimination, and the switching means switches theoutput path of the other packet received thereby from the branchingmeans based on the address control signal from the address controlmeans. Packet routing can therefore be conducted at higher speed than bythe conventional packet router that switches output paths in accordancewith address information after conversion from optical to electricaddress information.

The present invention further enables conversion of IP packet opticalcodes to be conducted optically.

An ultra-high speed, high-functionality photonic network can thereforebe realized by using the packet router at every node of a photonicnetwork.

1. A photonic network packet routing method comprising the steps of:optically encoding destination address information attached to anoptical IP packet into an optical code using light attributes;propagating the optical IP packet to a routing node; receiving theoptical IP packet at the node; discriminating the optical IP packet byestimating peak values of optical time correlations of the encodeddestination address information attached to the received optical IPpacket with encoded addresses; switching to an output path for theoptical IP packet based on a result of the discriminating step; andoutputting the optical IP packet labeled with prescribed addressinformation on the output path selected by the switching step, whereinthe optical encoding of the destination address information attached tothe optical IP packet comprises the steps of: dividing an optical pulseoutput by a pulse source into N number of chip pulses (N≧2) having aprescribed delay time therebetween; and changing intensity of theindividual chip pulses according to the coding method, and recombiningthe divided optical chip pulses.